As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open the packages described above, various solutions of opening devices have been proposed.
A first solution of opening device comprises a patch defined by a small sheet of a heat-seal plastic material, and which is heat sealed over a respective hole on the side of the web eventually forming the inside of the package; and a pull-off tab applied to the opposite side of the packaging material and heat sealed to the patch. The tab and patch adhere to each other, so that, when the tab is pulled off, the portion of the patch heat sealed to it is also removed to uncover the hole.
Alternatively, a second solution comprises closable opening devices which are applied by injecting plastic material directly onto the holes of the web. In this case, the application station is a molding station.
Finally, a third solution of opening device comprises a frame defining an opening and fitted about a pierceable or removable portion of the packaging material.
The pierceable portion of the package may be defined by a so-called “prelaminated” hole, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material. Also in this case, the application station is a molding station.
More precisely, web is provided with a plurality of prelaminated holes in a packaging material factory and then fed to the packaging machine.
Web is then wound off from a reel within the packaging machine. Subsequently, web is stepwise fed to the application station before that the packaging material is folded to form a tube. In particular, the web is fed towards the molding station along a first direction.
The molding of opening devices at the molding station requires that pre-laminated holes are fed in a correct position relative to the molding station.
However, due to several reasons, among which for example misalignments within the reel, the real positions of pre-laminated holes may differ from the theoretical positions, which are required for a correct molding of the opening device at the molding station.
Accordingly, it is necessary to adjust the position of the web before it reaches the molding station.
EP-A-122169 in the name of the same Applicant discloses a device for adjusting the position of the web of the packaging material on a packaging machine along a second direction, which is transversal to the first direction.
In greater detail, the web of packaging material is fed through the machine along a path defined by a plurality of drive or transmission rollers. The path is, in particular, parallel to the first direction.
The device comprises a slide movable along the second direction, a gripping member for gripping and moving the web in the second direction, and a motor for controlling the slide.
Device also comprises a pair of sensors for detecting the position of the web, and a control unit connected to the sensors and which controls the motor to move the slide along the second direction in response to the values detected by the sensors.
Due to the fact that it is at the same time both supported by fixed rollers and moved by gripping member relative to the rollers, the packaging material is subjected to stress and therefore may be damaged.
A need is felt within the industry to feed the application station with the packaging material having the areas at which the opening devices will be applied in the correct position while reducing the risk of damaging the packaging material.
Furthermore, the gripping member of the device disclosed in EP-A-122169 comprises a supporting plate hinged to the slide. The plate is fitted with an arm supporting a shoe cooperating in use with an edge of the web. The gripping member is subjected to the elastic force of a low-stiffness spring stretched between a fastening member and an auxiliary arm projecting transversely from plate. Plate also supports two shafts, which are fitted with idler rollers rolling on opposite side of web. Accordingly, gripping member is, in use, tilted forwards in a position defined by a balance between the action of the spring, the reaction of web onto shoes, and the frictional force between moving web and rollers.
A need is also felt within the industry to feed the application station with the packaging material having the areas at which the opening devices will be applied in the correct position while reducing the number of the overall components of the device.